Effects of Single Local Injection of Local Anesthetic Agents on Intervertebral Disc Degeneration: Ex Vivo and Long-Term in Vivo Experimental Study

Abstract

Introduction Discogenic low back pain (LBP) is generally caused by progressive intervertebral disc (IVD) degeneration associated with aging or trauma. Analgesic discography (discoblock) can be used to diagnose or treat discogenic LBP by injection of a small amount of local anesthetic. Lidocaine or bupivacaine is one of the most commonly used local anesthetics for discoblock. Several in vitro studies have reported dose- and time-dependent cytotoxic effects of these local anesthetics on IVD cells. In addition, a recent prospective, matched cohort clinical study showed that discography was associated with more extensive IVD degeneration at a 10-year follow-up. The present study aimed to investigate the deteriorating effects of lidocaine and bupivacaine on rabbit IVDs using an organotypic culture (ex vivo) model and an in vivo long-term follow-up model. Material and Methods Ex vivo study: The IVDs were surgically harvested from rabbits. A 0.9% saline solution, 1% lidocaine, or 0.5% bupivacaine was intradiscally injected using a microsyringe with a 26-gauge needle. IVDs were divided into five groups: untreated control, puncture-only group, saline group, lidocaine group, and bupivacaine group. After 3 or 7 days of the injection NP tissues were stained with propidium iodide (dead cell) and Hoechst 33342 (live and dead cells). NP cell death was evaluated using a confocal laser scanning microscopy ( n = 6). After 7 days of the injection histological analysis using hematoxylin and eosin (H&E) staining and TUNEL assays was performed on IVDs ( n = 6). In vivo study: Rabbit lumbar IVDs were percutaneously punctured under a fluoroscopic guidance. Overall, 15 µL of 0.9% saline solution, 1% lidocaine, or 0.5% bupivacaine was injected into IVDs (L2/L3 and L4/L5). L3/L4 was left intact as a control. A sham procedure was performed by subjecting control animals to IVD needle puncture only. After 6 or 12 months of the injection, midsagittal images of the treated discs were analyzed qualitatively for evidence of degenerative changes using a 7.0 T MRI. After MRI analysis, histological analysis was performed on IVDs using Safranin-O fast green and H&E staining. Semiquantitative evaluation of disc degeneration was also performed. Results Ex vivo study: Both anesthetic agents induced time-dependent NP cell death; when compared with an injected saline solution, significant effects were detected within 7 days. After 7 days, lidocaine and bupivacaine increased dead cells to 72 and 76%, respectively. The percentage of apoptotic NP cells in the lidocaine and bupivacaine groups was significantly higher than that in all other groups. In vivo study: MRI analysis showed no significant difference among the puncture, saline, and both anesthetic agent groups at 6 or 12 months. Histological assessment of IVDs revealed degenerative changes most severe in local anesthetic agent groups. However, there was no significant difference between the saline and anesthetic agent groups. After 12 months, there was a significant difference between anesthetic agent groups and untreated control groups in the number of NP cells. Conclusion Discoblock progressed IVD degeneration, but there was no strong evidence that the local anesthetics caused IVD degeneration in vivo rather than the initial mechanical damage of the pressurized injection.